• Anjan Kumar Sarkar

      Articles written in Journal of Astrophysics and Astronomy

    • Fisher Matrix-based Predictions for Measuring the z = 3.35 Binned 21-cm Power Spectrum using the Ooty Wide Field Array (OWFA)

      Anjan Kumar Sarkar Somnath Bharadwaj Sk. Saiyad Ali

      More Details Abstract Fulltext PDF

      We use the Fisher matrix formalism to predict the prospects of measuring the redshifted 21-cm power spectrum in different $k$-bins using observations with the upcoming Ooty Wide Field Array (OWFA) which will operate at $326.5 {\rm MHZ}$. This corresponds to neutral hydrogen (HI) at $z=3.35$, and a measurement of the 21-cm power spectrum provides a unique method to probe the large-scale structures at this redshift. Our analysis indicates that a $5 \sigma$ detection of the binned power spectrum is possible in the $k$ range $0.05 \leq k \leq 0.3 \, {\rm Mpc}^{-1}$ with $1000$ hours of observation. We find that the signal- to-noise ratio (${\rm SNR}$) peaks in the $k$ range $0.1- 0.2\, {\rm Mpc}^{-1}$ where a $10 \sigma$ detection is possible with $2000$ hours of observations. Our analysis also indicates that it is not very advantageous to observe beyond $1000$ h in a single field-of-view as the (${\rm SNR}$) increases rather slowly beyond this in many of the small $k$-bins. The entire analysis reported here assumes that the foregrounds have been completely removed.

    • Probing early Universe through redshifted 21-cm signal: Modeling and observational challenges


      More Details Abstract Fulltext PDF

      Cosmic dawn (CD) and the epoch of reionization (EoR) are the most important parts of cosmic history during which the first luminous structures emerged. These first objects heated and ionized the neutral atomic hydrogen in the intergalactic medium. The redshifted 21-cm radiation from the atomic hydrogen providesan excellent direct probe to study the evolution of neutral hydrogen (Hi) and thus reveal nature of the first luminous objects, their evolution and role in this last phase transition of the Universe and formation and evolution of the structures thereafter. Direct mapping of the Hi density during the CD–EoR is rather difficult with thecurrent and forthcoming instruments due to stronger foreground and other observational contamination. The first detection of this redshifted Hi signal is expected to be done through statistical estimators. Given the upmost importance of the detection and analysis of the redshifted 21-cm signal, physics of CD–EoR is considered asone of the objective of the upcoming SKA-low telescope. This paper summarizes the collective effort of Indianastronomers to understand the origin of the redshifted 21-cm signal, sources of first ionizing photons, their propagation through the IGM, various cosmological effects on the expected 21-cm signal, various statistical measures of the signal like power spectrum, bispectrum, etc. A collective effort on detection of such signalby developing e stimators of the statistical measures with rigorous assessment of their expected uncertainties, various challenges like that of the large foreground emission and calibration issues are also discussed. Various versions of the detection methods discussed here have also been used in practice with the Giant MeterwaveRadio Telescope with successful assessment of the foreground contamination and upper limits on the matter density in reionization and post-reionization era. The collective efforts compiled here has been a large part of the global effort to prepare proper observational technique, analysis procedure for the first light of the CD–EoR through the SKA-low.

    • Intensity mapping of post-reionization 21-cm signal and its cross-correlations as a probe of $f(R)$ gravity


      More Details Abstract Fulltext PDF

      We propose the intensity mapping of the redshifted Hi 21-cm signal from the post-reionization epoch as a cosmological probe of $f(R)$ gravity. We consider the Hu–Sawicki family of $f(R)$ gravity models characterized by a single parameter $f_{,R0}$. The $f(R)$ modification to gravity affects the post-reionization 21-cm power spectrum through the change in the growth rate of density fluctuations. We find that a radio interferometric observation with a SKA1-mid-like radio telescope in both auto-correlation and cross-correlation with galaxy weak-lensing and Lyman-$\alpha$ forest may distinguish $f(R)$ models from $\Lambda$CDM cosmology at a precision, whichis competitive with other probes of $f(R)$ gravity.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2022-2023 Indian Academy of Sciences, Bengaluru.